Continuous bleaching process



Patented Mme, 1938 UNITED STATES PATENT OFFICE 2,110,649 CONTINUOUS BLEACHING PROCESS Ehrhart Franz, Leipzig, Germany No Drawing. Application February 23, 1934, Se-

rial No. 712,609. In 1934 .12 Claims.

'means of such compounds artificial or natural material like cotton, wool, silk, nettle, jute, hemp, legumes, cereals, fats, fatty acids, horn, bone, artificial resin, artificial wool, artificial silk and similar material can be bleached. The hitherto prevailing method was to place the materials mentioned in raw or worked condition in a liquid constituting a usually alkaline solution of the bleaching agent concerned. After a time, the material to be bleached was removed from the solution, rinsed and dried. The bath was then provided with new bleaching agents if necessary and used again. In some instances, the material to be bleached was impregnated with the bleaching agent and the bleaching process completed by storing. The application of the latter method often resulted in relatively uneven bleaching, as

it happened quite frequently that some parts of the material to be bleached consumed the bleaching agentnear them more quickly than others,. though their bleaching was not co pleted When employing a bath, this drawbac could be overcome by passingthe bleaching liquor through the material to be bleached and thus compensating local differences in concentration, though even this method was not always successful, especially. when bleaching liquors of relatively low concentration were used. It was therefore dimcult till now to attain a certain degree of bleaching with certainty.-

According to the invention, care is taken dur: ing bleaching to prevent not only undesirable local reductions in concentration but also. a fall in the concentration of the entire liquor, since this fall may lead to total stoppage of the bleaching process and thus cause a considerable loss? of material and time. Continuous addition of bleaching agents is particularly advantageous when it is desirable or necessary to work with extremely low concentrations of bleaching agents),

, or when working at low temperatures. It is desirable to proceed in this manner, because higher concentrations of bleaching agents and higher temperatures involve a-very considerableattack on the material and thus a corresponding loss of the latter. By providing for continual contact .Germany February 1,

between the bleaching liquor and the material to be bleached uniformity in bleaching is promoted and the bleaching, which proceeds slowly in itself, accelerated, as fresh bleaching agents are always coming into contact with the material to 5' be bleached. It is of course also possible to increase the concentration of the bleaching agent slowly or step by step if necessary. Thebleaching process is preferably carried out in the following manneri First, the necessary temperature '10.

and concentration of the bleaching agent and, if necessary, the requisite increase of both during bleaching are ascertained by preliminary experi-. ments, whereupon bleaching begins and bleaching agents are continually added to such an ex- 15 tent thatthedesired concentration of the bleaching liquor is continually maintained, which can be controlled by occasional or continued analytical measurements. In certain cases, it is possible to find out from the course of the bleaching proc- 2o ess, and particularly from its retardation, that bleaching agents should be addedto stop this retardation. An especially good motion in the bath and thus very uniform and quick bleaching are attained by moving the bleaching liquor and 25 the material to be bleached towards one another, though this should not becarried out so as to cause damage to the material to be bleached, e. g., felting of the fibers to be bleached. 7

As the bleaching liquor will comparatively 30 often come into contact withthe walls of the bath, metal tubes, the circulating pump etc., and working conditions as a whole favor the rapid decomposition of the bleaching agent by catalytic and mechanical influences, it is preferable to use 35 the bleaching solutions in stabilized condition. For this purpose the customary stabilizers may be used with a few exceptions which will be dealt with below. It is a surprising fact that when stabilizers are used which are capable of lowering 40 I the pH-value of the solution the bleaching speed is not decreased, but in most instances even increased. The bleaching efiect, however, is affected by a side reaction which becomes apparent in the yellowing of the goods and which involves 45 a considerable loss of material. Practically, the bleaching passes therefore through an optimum, since bleaching efiect and yellowing follow one another rapidly and even proceed simultaneously, though yellowing, as a .rule, can be recognized 50 only later on, which applies especially to the bleaching of'the highly sensitive wool. .Owing tothis yellowing, most inorganic acids except phosphoric and boric acid were found to be absolutely unsuited to act as stabilizers; when sul furic acid is employed, yellowing cannot be prevented and starts practically when bleaching begins. Beside phosphoric and boric acids, the organic acids, especially oxalic and lactic acids, can be used which delay the appearance of yellowing so much that bleaching effects are attained which are equal to those obtained with an alkaline liquor, with the difierence, however, that the consumption of bleaching agents and material amounts only to a fraction of that of the alkaline process. In the interest of further increasing the bleaching speed in stabilized baths it is advisable 'to apply the bleaching agent in an activated state, so that the material to be bleached carries substances capable of accelerating bleaching at the points desired. Such substances include for instance metallic salts, enzymes and ferments as well as substances capable of imparting a high pH-value to an aqueous solution. Some of these compounds are easily soluble in water and will therefore after some time pass over into the bleaching liquor and compensate the stabilizers thereof or superpose them. If the bleaching liquor and the material to be bleached are then moved towards one another through the bath, the activator and the stabilizer will compensate one another and themost strongly activated material, i. e., the material at the moment entering the bath, will meet the most weakly stabilized liquor where the latter just leaves the bath. If this liquor is to be used again for bleaching, bleaching agents as well as stabilizers must be added thereto. The bleaching process described can be carried out in steps or combined with other bleaching processes, it being immaterial whether the process is carried out first or afterward or interposed. It is further possible to complete the bleaching begun in the bath by storing the wet material at normal or slightly increased temperature. Or the goods, having passed'the bath, may be guided directly over heated rollers for simultaneously bleachin and drying them. For moving the goods through the bath, devices like continuous belt conveyors or movable forks or grippers passing'through the bath may be used. If the material to be bleached has already the form of bands or pieces, such as the top of wool, it is advisable to pass these bands through the bleaching liquor after .the usual working. In case of such material, the required activator can be provided in the simplest way by allowing enzymes of the raw material to remain therein or by only incompletely removing substances like soap having an alkaline effect and being present from the pre-treatment prior to introducing the goods into the bleaching bath.

The following example is intended to explain the process according to the invention which,

and 0.5% fat is passed at a speed of 3.60 m. per

minute through a bath of non-catalyzing nonrusting metal like an iron-chromium-nickel alloy steel of 80 cm. lengthand" 100 1. capacity while bleaching liquor composed of 0.5% hydrogenperoxide and 0.01% oxalic acid is continually pumped through the bath at a speed of 10 l. per minute, hydrogen peroxide mixed with oxalic acid being continually added outside the bath before the liquor is returned to the bath. The wet material then passes hot rollers to complete bleaching and simultaneously effect drying.

5 Instead of one bath several baths connected in is further advantageous to make provision for,

having the bleaching agent and the material to be bleached run counter to one another, 1. e.,

to have the liquor run off where the material enters the bath, and vice versa.

In respect to specific arrangement of stabilizers and activators, see also my copending application: Bleaching process, Serial No. 710,527, filed February 9th, 1934; and concerning acidic peroxide bleaches, the copending application: Process for bleaching, Serial No. 712,608, filed February 23rd, 1934.

I claim:-

1. A continuous bleaching process which consists in treating organic material with acid stabilized aqueous solutions of bleaching agents containing up to 3% of H202, said material carrying at the points to be bleached substances capable of acceleratingbleaching and free from heavy metal, and in supplementing the bleaching agent during the process by adding the bleaching agent to the portion of the liquor which, during the addition, does not have to exert a bleaching influence upon the material to be bleached.

2. A continuous bleaching process which consists in treating organic material with acid stabilized aqueous solutions of bleaching agents containing up to 3% of H202, said material carrying at the points to be bleached substances capable of activating bleachingand consisting of compounds reacting alkaline in the presence of water, and in supplementing the bleaching agent during the process by adding the bleaching agent to the portion of the liquor which, during the addition, does not have to exert a bleaching influence upon the material to be bleached.

3. A' continuous'bleaching process which consists in treating organicmaterial with acid stabilized aqueous solutions of bleaching agents containing up to 3% of H202, said material carrying at the points to. be bleached enzymes as activators accelerating bleaching, and in supplementing the bleaching agent during the process by adding the bleaching agent to the portion of the liquor which, during the addition, does not have to exert a bleaching influence upon the material to be bleached.

4; A continuous bleaching process which consists in treating organic material with acid stabilized aqueous solutions of bleaching agents containing up to 3% of H202, oxalate-ionbeing added to stabilize the bleaching solution and for preventing yellowing, and in supplementing thebleaching agent during the process by adding the bleaching agent tothe portion of the liquor which, during the addition, does not have to exert a bleaching influence upon the material to be bleached.

5. A method of bleaching, comprising coating the material to be bleached with an activator, circulating a peroxide bleach, through a vessel, and, moving the material to be bleached through the bleach in the vessel counter to the direction of flow of the bleach.

6. A method of bleaching a material to be bleached and containing alkali introduced thereinto by a preceding treatment, comprising circulating an acid. stabilized peroxide bleach through avessel, and moving the material to be bleached through the bleach in the vessel counter to the direction of flow of the bleach.

7. A continuous process for bleaching a material carrying substances free from heavy metals for accelerating bleaching which comprises treat ing the material in a continuously circulating acid stabilized aqueous solution containing a bleaching agent or up to 3% H20: and continuously adding said bleaching agent to that portion of the solution which is circulated out of contact with said material to be bleached to maintain said bath at a predetermined concentration.- 1

8. A process according to claim. 'I, in which said substances consist of compounds reacting alkaline in the presence of water to accelerate the bleaching.

9. A process according to claim 7 in which said substances are enzymes for accelerating the bleaching.

10. A process according to claim '1 in which the bleaching solution contains the oxalate ion to stabilize the solution and prevent yellowing.

11. A continuous process for bleaching a material which comprises continuously circulating an acid stabilized aqueous solution containing a bleaching agent oi up to 3% H202, passing said material through said solution counter to the current of said solution, said material carrying substances for accelerating bleaching when it is passed through said solution, and maintaining said circulated solution at a predetermined concentration by adding said agent to a portion of said solution, which is out of contact with said material.

12. A continuous process for bleaching a material carrying a compound reacting alkaline in the presence of water to accelerate the bleaching which comprises treating the material in a continuously circulating acid stabilized aqueous solution containing a bleachng agent of up to 3% H202 and continuously adding said bleaching agent to that portion of the solution which is circulated out of contact with said material to be bleached to maintain said bath at a predetermined concentration.

EI-IRHART FRANZ. 

